Electric Skateboard – Completing skateboard #1

It’s taken a little longer than we had originally planned, but the first skateboard is finally complete! Aside from some minor adjustments, we have built an impressive machine that will hopefully have many kilometers of smooth riding in the months ahead… even if we have to wait until summer for the best of it.

A helmet is being used for all testing and riding. Greg couldn’t resist the first test ride.

It took a lot more work than we expected to create the missing pieces. You could say that is a plus, since it forced us to design some new solutions (new to us anyway). Thanks to some hard work from the team, all of the problems have been worked through… ready for version 2.0.

The main elements that we worked through were:

  1. The Gear-Mount (holds the large gear onto the wheel)
  2. The Motor-Mount (holds the motor to the rear axle)
  3. Painting the decks
  4. Mounting the battery-box onto the deck
  5. Configuring the motor controller
  6. Finishing (grip-tape on the top of the board, hooking up the battery level monitoring)

The Motor-Mount

Originally we planned to use an off-the-shelf (OTS) motor mount that could simply “bolt on” to the board. As soon as we opened the purchased parts we could see that there was no way that they would fit. The motor mount was designed to clamp onto a round “axle” (it’s not really the axle, but the horizontal part of the skateboard truck), and our “axle” was square. We tried grinding it down to a rounded cross-section, but the fit had other problems (like the motor we chose is bigger, and the drive-belt is longer). So designing and building a custom motor mount was a better option.

The Process. Having decided to build a custom motor-mount, we first needed to collect a detailed description of the requirements. Measurements were taken of the size & spacing of the holes on the motor. The gears were put inside of the drive belt so that we could get the optimal distance between the two gears so that the drive belt would be held at the right tension. Once we had the details of the holes needed for holding the motor to the plate, and the hole for the motor’s main axle (spindle), and the separation needed for the gears, we could estimate the location for the square hole that would be used to clamp the motor-mount onto the truck. With all of the important measurements, we sketched ideas for the mounting plate. The sketches eventually led to a final proposal that was neatly drawn up in a technical sketch with accurate dimensions. This is needed before starting work on making the actual motor-mount. BUT, this is only part of the ideal process that is used to avoid wasting time and materials on solutions that don’t work. In reality, we have to admit that it took 3 prototypes to create the “final” version that worked well.

The process used was roughly: collect measurements and requirements, sketches and explore the possibilities, detailed design and technical drawings, build prototype… rinse 🙂 and repeat.

Some early design sketches for the motor mount:

It’s important for the clamp to grip the axle tightly. The slot in the sketch below was added to help the material bend in a way that created the strong clamping force where it was needed.Preview of the final motor mount:

After carefully marking the location of the motor bolt slots onto a plate of aluminum alloy, holes were drilled.

The hydraulic punch-press was used to push out small squares of the material between the holes to create the slots. A larger square was pressed out of the aluminum plate, then carefully filed to the right size to snugly fit the axle. Before pressing out the square, holes were drilled at the corner locations to improve strength (sharp corners in holes focuses forces and makes it weaker, it also makes it easier to file flat sides on the square hole). Care was taken to remove material to enlarge the hole very slowly; it’s easy to take material away, but you can’t put it back. With all of the holes in the right places, the plate was cut away from the large plate (of stock) and shaped using saws and files. Designs for a 3rd prototype were also taking shape at the same time. A bolt was used to clamp the motor-mount in-place. A good result for a solid morning of work.

Mounting the Battery-Box

The custom-made 3D-Printed battery box was a very tight fit for the electronics components. The next version will be made slightly bigger to make it easier to assemble. One of the main problems with this version is that it is a lot of work if you want to disconnect everything from the battery. We had hoped that the electronics could stay connected and “on” for long periods. Unfortunately they use too much power on standby so there is a risk that eventually the battery could be over-discharged. More investigation is needed. For now, we just needed to mount the battery-box onto the skateboard. Four bolts were used: 2 bolts at the front are hidden, and they go through the board, the rear 2 mount-bolts screw into threaded metal inserts. Together with a weather-resistant sealing rubber strip, we mounted the electronics. Quite a neat result! …more detail coming soon.

This is the skateboard in action. A helmet is being used for all future testing 🙂